A multi-level cell (MLC) is a memory element capable of storing more than a single bit of information. MLC memories, such as MLC Flash and MLC Phase Change Memory (PCM), are typically read and written in an iterative manner. PCM is also known as PCME, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM. A programming step is typically followed by a verify step that verifies the intended value is stored at a particular address.
For example, MLC NAND Flash memory is a MLC Flash technology using multiple levels per cell to allow a plurality of bits to be stored using the same number of transistors. A typical MLC NAND Flash memory has four possible states or values per cell, so the cell can store two bits of information.
MLC PCM memory is a type of non-volatile memory that uses a semiconductor alloy having two states, crystalline and amorphous. The amount of material in each state changes the resistance of the MLC PCM memory cell. MLC PCM memory stores each binary bit using the various electrical resistances of the semiconductor alloy to program the various cell values. The phase, and thus resistance value, for each bit vale is controlled by applying a voltage to an address so that current may change the phase and represented value.